This invention relates to the automatic processing of liquids in open-ended containers for testing purposes, and more particularly provides an automated system for detecting Hepatitis B. Surface antigen (HB.sub.s AG) in human serum or plasma.
Many immunochemical reactions are performed by using what is known as a solid phase or phase separation system. Such analyses place one of the components on a solid support so it may readily be removed from the system during analysis. An example is the detection of HB.sub.s AG, wherein the antibody to HB.sub.s AG is affixed to solid controlled pore glass particles (CPG). Such CPG is mixed in a test tube with a patient's serum. The serum in a diseased patient contains antigen to hepatitis, and under proper conditions the antigen may be made to react with the antibody on the CPG. A typical operation includes the removal of other serum proteins from those hepatitis associated proteins which adhere biologically to the CPG. This separation involves the use of aqueous washes, such as saline or phosphate buffers which allow the extraneous proteins to be removed without disturbing the chemical bond between the antigen and the hepatitis-associated proteins on the CPG. Identification markers or labels are also added in this analysis, but the excess quantity of these reagents usually must be removed also by washing or other phase separation techniques.
In performing a typical hepatitis assay, a patient's serum is incubated or mixed with CPG so that the required chemical reaction takes place. Next, buffer is added to and agitated with the patient's sample, and following agitation the CPG settles to the bottom of the test tube. Following settling, the liquid in the tube is aspirated or otherwise withdrawn, with the CPG remaining in the tube. Such buffer addition-agitation-removal may be repeated a number of times to remove most of the extraneous proteins. To verify the presence of an antigen adhering to the CPG, a label is added to the test tube which may be identified as, for example, by a coloring agent, an enzyme multiplication agent, or radioactive tag or a fluorescent agent incubation of the tagged label with the antibody antigen complex on the CPG forms a "sandwich". After a suitable incubation period, the excess label is removed by a wash in generally a number of washing steps. The material adhering to the CPG in the tube, as a sandwich, yields an indication which may be compared to known positive or negative controls to identify the patient's serum.
The operations outlined above are described in the brochure RIAUSURE.sup..RTM. II published by Electro-Nucleonics Laboratories, Inc. These operations are tedious and require manual dexterity and continued operator attention to be properly carried out. The danger from operator fatigue and mistake, leading to false identification of a sample, is always present. In addition, variations in test parameters can occur from one test to another, leading to varying results.
It is desirable to optimize any immunochemical analysis by choosing proper conditions. While generally it is desirable to decrease the size of the CPG and the serum-carrying container (because the kinetics of the reactions will be faster and more reliable), the reduction of size creates problems in the manual handling of the tests, leading to errors.
The present invention provides for the automating of the HB.sub.s AG test procedure. It proceeds from the RIAUSURE.RTM. procedure of Electro-Nucleonics Laboratories, Inc. That procedure provides agitation and settling according to a programmed time schedule using small ferrite magnets placed inside each of the assay tubes. The test tubes are placed on an electro-magnetic assembly containing field coils energized by a digital counter, producing a varying field causing the magnets to move within the test tube and thereby agitate the serum-buffer-glass system within each tube. At an appropriate time, the magnetic field is deenergized, allowing the magnets to rest at the bottom of the test tubes, leaving a clear, supernatant liquid thereabove. A multiple head aspirater is employed to withdraw the supernatant liquid from the test tubes; a separate multiple head dispenser is used to introduce liquid along the wall of each test tube. The above cycle is completed manually and repeated until the tubes are properly washed. An appropriate label is added manually to each tube.
In the present invention, a card is utilized to hold a number of test tubes (e.g., twenty test tubes). The tubes are open-ended at the top thereof, and are carried by the card so that the bottom portions thereof extend below the card. The card rests on a carrying block, and the lower portions of the containers extend loosely into openings in the block. In this fashion, the test tubes are carried loosely by the block, facilitating later operations, as described below. A number of such blocks are positioned on a support table and are moved thereon in step-wise fashion around the table. Each tube contains a sample of a patient's serum along with magnetic particles, and underlying the table is a series of coils, the magnetic fields from which cause agitation of the magnetic particles and an appropriate mixing of the liquids within the test tubes. The test tube-containing blocks are caused to move in a rectangular pattern around the table in step-wise fashion by moving pins. The positions on the table provide for incubation, washing, label addition, detection, storage, and instrument cleansing. The washing assembly for adding a washing liquid to the test tubes and removing that liquid therefrom utilizes supply and aspirating heads positioned above the test tubes and movable vertically thereover. To process a number of test tubes simultaneously, the supply head includes a number of liquid supply tubes that communicate with a liquid supply manifold within the head. The aspirating head includes a plurality of aspirating tubes communicating with a vacuum chamber within the aspirating head. The aspirating and supply heads are movable vertically with respect to each other. Preferably, the supply tubes extend at an angle with respect to the vertical so as to wash the sides of the test tubes, and terminate within the supply head. The aspirating head is movable to move the aspirating tubes to positions in which they extend through and below the supply head and into the test tubes for aspirating liquid therefrom. To facilitate holding the test tubes, the supply head includes a test tube engaging portion in the lower part thereof for engaging the open ends of the test tubes. That lower portion of the supply head is movable vertically within the supply head and is yieldably biased to a lower position, moving upwardly upon engagement of the supply head with the test tubes. The supply head includes passages therein in which the supply tubes are positioned, and other passages for containing the aspirating tubes from the aspirating head thereabove. These passages terminate in a frusto-conical opening of increasing diameter to facilitate the positioning of the open-ended test tubes therein, facilitated by the loose holding of the test tubes in each carrying block.
Provision is made for washing the aspirating tubes to avoid carryover of contaminants.
Label addition is carried out by a label adding head preferably carrying two syringes, one for each of two rows of test tubes carried in a card. This head is moved vertically and horizontally to receive label and to dispense that label into the test tubes. The syringes are driven so that there is a slight drawing motion after each dispensing operation to prevent droplet leakage from the syringes.
Following passage of the test tubes through the system, the tubes are inspected, for example, by an appropriate radiometric or colorometric test.
The invention will be more completely understood by reference to the following detailed description which is to be read in conjunction with the attached drawings.